Genetics: practice question

A Pediatrics question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Pediatrics · Genetics

Sample item

A toddler has severe hypotonia and feeding difficulty in infancy, and now has hyperphagia, obesity, hypogonadism, short stature and almond-shaped eyes. What is the underlying genetic abnormality?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Loss of paternal chromosome 15q11-q13 expression

Prader-Willi syndrome results from absence of the paternally derived 15q11-q13 region by deletion, maternal uniparental disomy or imprinting defects. Infants are hypotonic and feed poorly, then develop hyperphagia and obesity. Loss of the maternal copy of the same region causes Angelman syndrome.

Option by option

  • A. Trisomy 21

    Trisomy 21 has different features such as a single palmar crease and congenital heart disease.

  • B. Loss of paternal chromosome 15q11-q13 expression (correct)

    Correct. Paternal deficiency, because the maternal copy is imprinted and silenced, produces this syndrome.

  • C. Loss of maternal chromosome 15q11-q13 expression

    Loss of maternal expression causes Angelman syndrome with seizures and happy demeanour.

  • D. Monosomy X

    Monosomy X is Turner syndrome in girls.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Pediatrics question

What is the answer to this Pediatrics question?

The best answer is B, Loss of paternal chromosome 15q11-q13 expression. Prader-Willi syndrome results from absence of the paternally derived 15q11-q13 region by deletion, maternal uniparental disomy or imprinting defects.

Why is "Trisomy 21" not the answer?

Trisomy 21 has different features such as a single palmar crease and congenital heart disease.

Why is "Loss of maternal chromosome 15q11-q13 expression" not the answer?

Loss of maternal expression causes Angelman syndrome with seizures and happy demeanour.

Why is "Monosomy X" not the answer?

Monosomy X is Turner syndrome in girls.

What concept does this question test?

It tests Genetics in Pediatrics. Infants are hypotonic and feed poorly, then develop hyperphagia and obesity. Loss of the maternal copy of the same region causes Angelman syndrome.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Genetics?

Memorise milestones and the vaccine schedule as tables and revise them often. Then use the flashcards and the other Pediatrics questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.